GPX/FIT file comparison

Fit file says


Gpx says

Have you got Garmin Basecamp? Load the FIT and GPX into that in a same folder, see if you get similar?

Thanks for this new thread! However, I have to get up again in 5 hours, and leave the topic to you for the next few hours ;)

Git :) ... you know I'm like a dog with a bone!

I'm going to see if basecamp can strip out the elevation data from the GPX and the FIT, lock it to the maps DEM profile and see which one is locked to DEM!

Colour me confused.

Basecamp can export the FIT and GPX as CSV.

Even though they show a different ascent/descent (which really does suggest to me this is elevation based)

Elevation and position seem identical for both files....

Argh.... missing something here

FIT FILE says ascent 117 descent 187
GPX FILE says ascent 131 descent 201m

Yet if Basecamp converts the FIT to a GPX and reimports it it keeps the same asc/desc as the original fit.

So there's something weird here. Trying to find where it's calculated asc/desc because that's (to me) the root cause of this

At a loss, but I wonder if you people with the more extreme distance differences between GPX and FIT... do you see a similar large discrepancy in Ascent and Descent - that may go part of the way to explaining the difference in distance....

Thanks for moving this discussion. Anyway, not to sound stupid, I know a FIT file is just basically a copy of my workout.  What is a GPX file and why are some seeing discrepancy with distance between the two?  I guess what I was saying to bluefish in the other thread is even if I knew how to import a GPX file, it wouldn't matter to me what the distance said as I trust and know my calibrated wheel is correct.  I work cable maintenance for a major communications company.  I can set the temperature and cable gauge on my meter and TDR (Time Domain Reflectometry) or RFL (Resistive Fault Location) to find the distance to a known fault.  It's then measured out to that location for repairs, so I know the wheel is spot on for distance. 

GPX and FIT files are just different ways of exporting the data - different file formats - think much like PNG and jPG are both images.

The way the data is stored within SHOULD be identical, but what we're seeing is some difference.

I THINK (and I must emphasise THINK) that one of these files holds the exact position and altitude as per the GPS reading made at the time, and the other holds the location as the location of that POSITION on the planet.

Now all GPS have slight errors, so lets say (for discussion) the error is 1 metre. And we're running on a flat surface 200m above sea level.

So for a set of readings, lets say the GPS was consistently too high (by this 1 metre) for 10 readings

The one file would have elevation

200,200,200,200,200,200.... as it stores the altitude merely as the altitude of the ground there

The other would have 

201,201,201,201,201,201.... as it stores the GPS reading of elevation.

Now over a long distance, this could add up if for example the next time you ran it, the altitude read by the GPS went

201,199,201,199,201,199

It's a bit of an intellectual argument type thing, but what I am seeing for the GPX and the FIT files is a difference in total Ascent and Descent.

Now I'm seeing less than a 1% error in both, which is within GPS tolerances. But others aren't

It's also why I asked if people had run a measured route - say exactly 10K. To serve as your "calibrated wheel" in this example. Then run the course precisely from stop to finish, and compare the output of both files.

If you run a measured 10K exactly - and your FIT file (the main format) says 9.99K and the exported GPX (which will have been processed or smoothed in some way perhaps) comes up at 10.2K - then I'm more likely to say the file conversion from FIT -> GPX is introducing a systematic error